Effect of additives on the properties of plasma electrolytic oxidation coatings formed on AM50 magnesium alloy in electrolytes containing K2ZrF6

A plasma electrolytic oxidation (PEO) coating on AM50 magnesium alloy was obtained in a K2ZrF6–NH4H2PO4–KF–C6H5O7Na3 electrolyte solution. The influence of the electrolytes on the properties of the PEO coating had been investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), roughness determination and electrochemical measurements. The experimental results show that 10 g L− 1 K2ZrF6 and the presence of 8 g L− 1 NH4H2PO4 are beneficial for the passivation effect of the solution on AM50 Mg alloy as well as the compactness of the PEO coating. Many pores with large dimension on the surface of the coating are filled with coating compounds (mainly MgF2), and the characteristics of these pores are influenced by the concentration of KF. The addition of KF and C6H5O7Na3 enhances the growth rate of the coating. The coating shows high corrosion resistance in the presence of 10 g L− 1 K2ZrF6 combined with 8 g L− 1 NH4H2PO4, 3 g L− 1 KF and 5 g L− 1 C6H5O7Na3.